1. Field of the Invention
The present invention relates to nonaqueous electrolyte batteries.
2. Description of the Related Art
In recent years, the market for portable information devices, such as mobile phones and electronic mail terminals, has been rapidly expanding. Furthermore, in view of environmental concerns and the energy crisis, there has been an increased interest in hybrid vehicles and electrical automobiles. Under these circumstances, there have been demands for high-energy electrical storage devices.
Lithium has a standard reduction potential of −3.05 V and is easily ionizable metal in the electrochemical series. That is, an electrical storage device having a negative electrode composed of lithium has a high operating voltage and a high level of energy. On the other hand, since lithium has the lowest atomic weight among metals, the theoretical capacity of lithium is very high at 3,862 mAh/g. Consequently, when lithium is used as a negative electrode, an electrical storage device having a high energy density can be obtained.
Meanwhile, metal/air batteries are known in which a metal is used as the negative electrode active material, and oxygen in air is used as the positive electrode active material. Since oxygen is supplied from the outside, the metal/air batteries can be high-capacity electrical storage devices. Air batteries in which lithium is combined with air are referred to as lithium/air batteries, and have been recently receiving attention as high-energy electrical storage devices (for example, Japanese Unexamined Patent Application Publication Nos. 2005-166685 and 2006-286414). For example, with respect to a lithium/air battery described in Japanese Unexamined Patent Application Publication No. 2005-166685, it is reported that when discharged at a current density of 0.5 MA/cm2, a discharge capacity of about 10 to 15 mAh is achieved. Furthermore, magnesium/air batteries in which magnesium is used instead of lithium have also been proposed (for example, Japanese Unexamined Patent Application Publication No. 2003-7357). In such lithium/air batteries, the electrochemical reaction of oxygen occurs at the positive electrode, lithium peroxide and lithium oxide are generated during discharging, and these oxides are decomposed to produce oxygen gas during charging.
Furthermore, zinc/bromine batteries which are metal/halogen batteries and in which zinc is used as the negative electrode, and bromine is used as the positive electrode have been known for a long time (for example, Japanese Unexamined Patent Application Publication Nos. 7-14617, 5-182653, and 4-223049).